The present invention relates generally to feedback controllers and more particularly to systems and methods for calculating performance indices for feedback controllers. The present invention may be implemented in a building heating, ventilation, and air conditioning (HVAC) system to monitor and quantify the performance of the HVAC system.
Feedback controllers are used to control a wide variety of systems and processes. In a building HVAC system, feedback controllers are used to control HVAC devices (e.g., valves, pumps, dampers, fans, chillers, air-handling units, etc.) in a way that maintains a controlled variable (e.g., temperature, humidity, flow rate, pressure, etc.) at a desired setpoint. Feedback controllers generally use control parameters such as a proportional gain, an integral term, and/or a derivative term. The control parameters may be applied to an error signal (e.g., a difference between a setpoint and a feedback signal) to calculate an input that is provided to the controlled system or process.
The performance of a control system depends significantly on the performance of the controller. Various methods have been used to quantify the performance of feedback controllers. However, many traditional performance measures (e.g., mean absolute error) have expected values that depend on the system under control, as well as the size and frequency of unmeasured disturbances. Such performance measures are difficult to evaluate and cannot be directly compared across systems or controllers. Other performance measures use an idealized benchmark (e.g., minimum variance) to generate normalized performance indices. However, traditional methods for calculating normalized index values are computationally expensive and the use of such methods has generally been limited to analyzing data offline in batch.